Allan Chester Johnson was known for his work as a historian of ancient municipal organization, and particularly his book on municipal administration in ancient Rome. In this essay he addresses the puzzling problem of the creation of the tribe Ptolemais in Athens. The people of Athens were divided into tribes for the purposes of voting, and several new tribes were added in the 3rd century BC for reasons that are not explicitly recorded in the literary record. Johnson uses his extensive abilities in epigraphy to fill this gap, providing tables of data that will prove useful to scholars with an interest in the civic administration of Athens in the Hellenistic era.